. A textbook of botany for colleges and universities ... Botany. 262 MORPHOLOGY. becomes curved, the micropyle being directed thus towards the surface of origin; such ovules are called campylotropoiis (fig. 583), and they are much less common than the other kinds. Far the most common kind of ovule among angiosperms is one which develops a stalk (funiculus) that becomes curved at the apex, so that the body of the ovule lies against it, and although the axis of the body is straight, the micropyle is directed towards the surface of origin; such ovules are called anatropous (in- verted), the funic
. A textbook of botany for colleges and universities ... Botany. 262 MORPHOLOGY. becomes curved, the micropyle being directed thus towards the surface of origin; such ovules are called campylotropoiis (fig. 583), and they are much less common than the other kinds. Far the most common kind of ovule among angiosperms is one which develops a stalk (funiculus) that becomes curved at the apex, so that the body of the ovule lies against it, and although the axis of the body is straight, the micropyle is directed towards the surface of origin; such ovules are called anatropous (in- verted), the funiculus appearing as a ridge along one side of the body of the ovule (figs. 581, 584). The advantage of the anatropous ovule may be recognized when it is remembered that the pollen tube is advancing along the wall of the ovary, and the micropyles are thus brought near the wall. Development. — The megasporangium (really the nucellus) is eusporangiate in its development, resembling the microsporan- gium at every stage. There is usually a single hypodermal initial cell, which is soon recognized among the other h)rpodermal cells by its larger size and the different ap- pearance of its contents (fig. 585). Some- times there are two or more of these initial cells, as is the usual case in microsporangia. The large hypodermal initial divides by a periclinal wall into two cells, the outer cell' into primary wall cell (outer being the primary wall cell, the inner on^ shaded one) and primary spo- being the primary sporogenous cell (fig. 586). rogenous cell.—-After Cham- rrii n 11 ^ ji- -ji /n n \ BE^LAIN. ^°^ ^^'' ^^^^ ™^y "°^ '^'^•'^^ (^S- 587), or there may be one or more divisions (fig. 588), or in some cases there may be several wall layers developed, as in microsporangia. The primary sporogenous cell does not divide^and form more sporogenous cells, and therefore it is the megaspore mother cell. This means that when it divides, a tetrad is formed by two successive division
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